calculate_isi_caumo: Caumo OGTT Insulin Sensitivity Index Calculation (from...

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Caumo OGTT Insulin Sensitivity Index Calculation (from standard 75g OGTT)

Description

This function calculates the Caumo Insulin Sensitivity Index using glucose and insulin sampled during a standard 75g oral glucose tolerance test.

Usage

calculate_isi_caumo(
  time,
  glucose,
  insulin,
  weight = NULL,
  f = 0.8,
  dose_glucose = 75,
  time_units = "min",
  glucose_units = "mg/dl",
  insulin_units = "uU/ml",
  weight_units = "kg"
)

Arguments

time	a column name (unquoted) indicating time values (in minutes); first value assumed to be t=0
glucose	a column name (unquoted) storing glucose values (in mg/dL)
insulin	a column name (unquoted) storing insulin values (in uU/mL)
weight	Body weight, in kg
f	Fraction of Glucose absorbed (default 0.8)
dose_glucose	Glucose Dose, in grams (default to 75g, standard OGTT)
time_units	if units are not in "min", can indicate here for unit conversion (options "min" or "hr")
glucose_units	if units are not in "mg/dl", can indicate here for unit conversion (options "mg/dl" or "mmol/l")
insulin_units	if units are not in "uU/ml", can indicate here for unit conversion (options "uU/ml" or "pmol/l")
weight_units	if units are not in "kg", can indicate here for unit conversion (options "lbs" or "g")

Details

Standard timepoints are 0, 30, 60, 90, and 120 min. Note: insulin unit conversion may differ differ depending on assay. Insulin (pmol/l) = insulin (uU/ml)*6

calculate_isi_caumo() accepts 3 separate vectors for time, glucose, insulin. Other options include f (absorption fraction), and D (glucose dose)

Uses the formula detailed in Caumo et al:

\frac{f \cdot D_{oral} \cdot \frac{AUC[\Delta g(t)/g(t)]} {AUC[\Delta g(t)]} - GE \cdot AUC[\Delta g(t)/g(t)]} {AUC[\Delta i(t)]}

Where g(t) is glucose and i(t) is insulin during the time course. GE is assumed to be 0.024 dL \cdot kg^{-1} \cdot min^{-1}, f=0.8, and D = 75g (standard OGTT glucose dose). The values for f and D can be changed if desired.

Value

Caumo Insulin Sensitivity Index as a single value (10^5 dL/kg/min per pmol/L)

Examples

# individual objects for each item
time=c(0, 30, 60, 90, 120)              # minutes
glucose=c(93, 129, 178, 164, 97)        # mg/dL
insulin=c(12.8, 30.7, 68.5, 74.1, 44.0) # uU/mL
calculate_isi_caumo(time, glucose, insulin, weight=70) # 9.9

# handling data stored in a dataframe
ogtt1 <- data.frame(time=c(0, 30, 60, 90, 120),              # minutes
                    glucose=c(93, 129, 178, 164, 97),        # mg/dL
                    insulin=c(12.8, 30.7, 68.5, 74.1, 44.0)) # uU/mL
calculate_isi_caumo(ogtt1$time, ogtt1$glucose, ogtt1$insulin, weight=70)

# Example MTT values from Caumo JCEM 2000
ogtt_240 <- 
data.frame(
  time = c(0L,10L,20L,30L,40L,50L,60L,75L, # min
           90L,120L,150L,180L,210L,240L),
  glucose = c(91.20261837,90.66992397,108.3909704, # mg/dL
              139.8847729,152.5975273,143.3663292,129.5222883,
              112.3147056,101.7628589,89.75299304,89.80197787,86.49105416,
              86.07894263,85.66752014),
  insulin = c(9.999828359,11.48044146,30.08866995, # uU/mL
              67.20760028,80.39017525,92.0833834,88.67015671,
              69.61466504,52.58035392,35.53244881,30.61193594,21.64875303,
              12.36703798,9.680575342))
with(ogtt_240, calculate_isi_caumo(time, glucose, insulin, weight = 70))
with(ogtt_240, calculate_isi_caumo(time, glucose, insulin, 
weight = 154, weight_units="lbs"))
with(ogtt_240, calculate_isi_caumo(time, glucose, insulin))

JMLuther/tabletools documentation built on April 14, 2025, 3:09 a.m.